The Shaykh gave an example of a scholar sometimes falling into contradiction in authenticating and weakening hadiths, and he used himself as the example.

The Shaykh : ... And I am not taking you far; I will give you an example of myself; so that you do not say that the Shaykh does not make mistakes, but rather the Shaykh does make mistakes, but his mistake is better than the mistake of others; because he researches and exerts effort, and so on, so he is bound to fall into a mistake, whereas the one who does not research will have many mistakes. What is the example? Just now; pardon me, yesterday or the day before yesterday, a man from our brothers, the students of knowledge, from Aleppo came to me, and drew my attention to one hadith. I say this so that you correct what you have. One hadith exists in my book "Sahih al-Jami'" and "Da'if al-Jami'". The first thing that came to my mind was that this type has many examples in the two books, but upon research and verification, it appears that the one drawing our attention is the one who made the mistake. The reason is that the hadith is in one book with one wording, and in the other book with another wording, and in one of them there is something not in the other; and therefore one of them was placed in the Sahih and the other was placed in the Da'if. This is part of the precision of knowledge. But when he showed me the text, it was not of this type at all. The text is ; this is the text of the hadith or its meaning. We included it in the Sahih, and we included it in the Da'if. I told him: Leave the matter to me so that I study the issue calmly and with deliberation.
In one of the books, I attributed the hadith to "Silsilat al-Ahadith al-Sahihah", meaning: a double error; because the error is based on an error. I included one of the hadiths in "al-Sahihah", and I included the other in "al-Da'ifah". When I went back, I found the chain of narration to be the same! Do not be surprised if scholars of hadith differ among themselves. I am not contradictory. I found the chain to be the same, but I quickly realized the mistake. The mistake involves two men—and this is one of the causes of disagreement among scholars of hadith—two men have the same name and the same father's name. The name of each one resembles the other with his father's name: 'Abd Allah ibn Waqid, 'Abd Allah ibn Waqid, they are two. One is from Harran, and the other is from Herat. The famous one in the books of hadith and the chains of hadith is the one from Harran, and his kunyah is Abu Waqid. I will not hide from you, so that you understand me well from my negligence, that 'Abd Allah ibn Waqid comes in the hadith with his kunyah. And who is he? Abu Waqid? No, pardon me; he came with the kunyah Abu Rajaa. So 'Abd Allah ibn Waqid, Abu Rajaa, is trustworthy, whereas 'Abd Allah ibn Waqid, Abu Waqid, is weak. So I was negligent in seeing the kunyah Abu Rajaa for 'Abd Allah ibn Waqid, and I went on saying: 'Abd Allah ibn Waqid is weak, without detail and without... without what? Without sources. So we weakened the hadith. In "al-Sahihah", I was aware that 'Abd Allah ibn Waqid is Abu Rajaa, and he is trustworthy, so we put it in the Sahih. When the brother came, I showed him the reason for this mistake. This is one person who falls into such a thing, so it is even more likely that one person falls into the mistake I made, and another falls into the correctness I reached, and so on.
So the reason—also—we can summarize it as follows: this one looks at a path of the hadith that the other did not look at, so he authenticates it, and that one looks at a hadith whose chain is weak, so he weakens it. But if they met and understood each other, they would agree on the authenticity of the hadith. And there are many reasons; suppose the chain is the same, one authenticates it and one weakens it, and the narrator is the same, not like our friend Abu Waqid here; the reason would be that the biographer of one of the two men found a certification of his trustworthiness, and the other found a weakening, but the weakening is stronger than the certification, or it could be the opposite.
The important thing is that if this question has a benefit to be expected from it, it is to alert the attendees to two things: First, that disagreement is a natural matter among humans; and therefore we never hold it against the imams of fiqh, just as we do not hold it against the imams of hadith in what they disagreed upon; because this is a natural matter, and the causes are natural, cosmic, and the Sunnah of Allah in His creation. But we take that as a means to draw people's attention to the fact that they must learn and must exert effort just as the previous imams exerted effort; whether they were among the scholars of fiqh, or among the scholars of hadith. And when the fuqaha increase in the ummah and the muhaddithin increase among them as well, disagreements decrease; whether they are fiqh disagreements or hadith disagreements. But when there is only one person in fiqh in a field in some countries, he is exposed to error, and there is no one to point out his error to him; therefore I am very happy when I feel now that there are among our brothers in this town and elsewhere who point out my error to me; because I have come to feel that we have begun to reap the fruits of spreading the Sunnah among people, and the science of hadith and the terminology of hadith. Whereas previously, and without a doubt, like any beginner in any science, I made many mistakes and there was no one to alert me; why? Because I lived in this science alone.
So we ask Allah—Mighty and Majestic—to awaken the Islamic ummah to understand their religion by relying on the Book and the Sunnah, and to inspire groups among them to perform the duty of this correct understanding, and to study the science of the Sunnah with a correct scientific study.
And this is sufficient, and praise be to Allah, Lord of the worlds.